The present invention relates to a magnetic core for a flying-type composite magnetic head for use in a magnetic disk drive in such a manner that it is slightly floating over a magnetic recording medium.
As magnetic heads used for writing and reading information in magnetic disk apparatuses, flying-type magnetic heads as shown in U.S. Pat. No. 3,823,416 and Japanese Patent Publication No. 57-569 are widely used. Such a flying-type magnetic head is constituted by a slider, a tail end of which is provided with a magnetic gap, and the overall slider body is constituted by an oxide-type magnetic material with high permeability.
The flying-type magnetic head is in light contact with a magnetic disk by a spring force when the magnetic disk is stationary, but when the magnetic disk is rotating, a flow of the air over the magnetic disk exerts an upward force to a lower surface of the slider, whereby the magnetic head floats over the magnetic disk. When the magnetic disk starts to rotate or stops, the magnetic head comes into sliding contact with the magnetic disk. The contact condition of the magnetic head with the magnetic disk when the magnetic disk is stopped will be explained in detail. First, the flow of surface air becomes gradually slow when the rotation speed of the magnetic disk is reduced. And when the magnetic head loses its floating force, it collides with the disk surface and jumps up by its reaction and then falls onto the disk surface again. Such movement is repeated and the magnetic head slides on the disk to finally stop. Accordingly, the magnetic head should withstand shocks at the time of start and stop, and such characteristics are sometimes called CSS characteristics (contact start stop characteristics).
Flying-type magnetic heads conventionally were constituted by ferrite which is an oxide-type magnetic material with high permeability have relatively good CSS characteristics. However, but the ferrite has a small saturation magnetic flux density, so that sufficiently high recording densities cannot be achieved to recording media having high coercive forces. Specifically, even with Mn-Zn ferrite having a relatively high saturation magnetic flux density Bs, its Bs is at most 5000 G or so.
It was then found that to achieve Bs of 8000 G or more, a magnetic head is desirably provided with a thin magnetic metal layer in its magnetic gap. For instance, Japanese Patent Laid-Open No. 58-14311 proposes a flying-type magnetic head composed of ferrite and provided with a magnetic metal layer with high saturation magnetic flux density only in a magnetic gap portion thereof. However, in this magnetic head, a magnetic transformation part has large inductance after provided with coil windings, so that it has low resonance frequency. This means that it is disadvantageous in recording and reproducing at high frequency. Here, the large inductance is due to the fact that the overall magnetic head is composed of a magnetic material. Accordingly, to achieve low inductance, a magnetic circuit should be made small. From this point of view, U.S. Pat. No. 3,562,444 discloses a flying-type composite magnetic head in which a magnetic core is embedded in and fixed to a non-magnetic slider, without constituting the entire magnetic head with a magnetic material.
Further, the present inventors proposed in Japanese Patent Laid-Open No. 61-199219 a flying-type magnetic head in which a magnetic core is embedded in a non-magnetic slider.
It has been found from the above that to obtain a flying-type composite magnetic head having good recording characteristics to high-coercive force recording media and small inductance, a magnetic core should be constituted by a Mn-Zn ferrite substrate with a high saturation magnetic flux density Bs and coated with a thin magnetic layer having high Bs in its magnetic gap portion, and such magnetic core should be embedded in a non-magnetic slider. An example of such magnetic heads is shown in Japanese Patent Laid-Open No. 60-154310 by the present inventors.
Further, Japanese Patent Laid-Open No. 61-199217 proposed a magnetic head in which a magnetic gap portion of a magnetic core is in an X-shape. In this X-shaped magnetic gap, however, each core piece has a sharp tip portion coated with a high-Bs magnetic thin layer and ground in parallel for defining the magnetic gap. Accordingly, to obtain a desired track width, the high-Bs magnetic thin layer should have a somewhat large thickness.
Proposed as a magnetic core free from such restriction is a so-called parallel-type magnetic core constituted by a pair of core pieces having flat opposing surfaces and having a track surface provided with a notch for restricting a track width of the magnetic core. The parallel-type magnetic core is generally constituted by an I-shaped core piece and a C-shaped core piece, and the I-shaped core piece is usually provided with a thin magnetic metal layer made of Fe-A.+-.-Si, etc. The parallel-type magnetic core is advantageous in that a magnetic gap is easily formed.
However, since the thin magnetic metal layer and the core piece generally have largely different thermal expansion coefficients, the thin magnetic metal layer tends to peel off from the core piece, or the core pieces are likely to be cracked due to internal stress in a bonding portion with the thin magnetic layer, when the core pieces are bonded with each other by glass, or when the magnetic core is fixed to a non-magnetic slider. Further, when a thin magnetic metal layer is formed in a window portion of the magnetic core for winding, the thin magnetic metal layer is likely to peel off at the time of winding.
Various attempts have been made to solve the above problems. For instance, to prevent the problems of peeling and cracking due to the difference in thermal coefficient between the core pieces and thin magnetic metal layer, the thinning of the metal layer is considered. However, it is not preferable to make the metal layer extremely thin because it leads to the deterioration of its magnetic properties. Further, it may be possible to form the thin magnetic metal layer only in a magnetic gap and a back gap, but it is generally extremely difficult to form the thin magnetic metal layer only in the magnetic gap portion and the back gap portion of an extremely small magnetic core by a sputtering method with a high precision.
In addition, the formation of the thin magnetic metal layer partially on one core piece of the magnetic core is usually conducted by using a mask shown in FIG. 9. The mask 91 has a structure as shown in FIG. 9, and it covers a ferrite core block 92 contained in a holder 93. FIG. 10 shows in detail the mask 91 arranged on the core block 92 contained in the holder 93. In this state, the thin magnetic metal layer is formed by sputtering. Thus, as shown in FIGS. 11 (a) and (b), end portions of the resulting thin layer 94 become thin due to a shadow effect, or due to the phenomenon that the mask 91 is raised slightly. These thinned or tapered end portions of the thin layer 94 cause the problem that a magnetic gap length becomes larger toward the end portions of the thin layer, thereby changing the characteristics of the magnetic core.